Viewing experiences of contents that have been originally carried out in one direction, such as broadcasted television programs, are becoming bidirectional, which means that viewers carry out some activities with respect to contents because of diversification of contents provision means and diffusion of information transmission means such as social media in recent years. For example, Patent Literature 1 discloses a technology for presenting comments submitted to an external sharing website to viewers viewing a program that is currently broadcasted, thereby providing a bidirectional viewing experience to the viewers.